Process for producing chlorides of chromium and iron from chrome ore



Sept. 8, 1970 TAGAYASU UNO ET AL 3,527,561

* PROCESS FOR PRODUCING CHLORIDES OF CHROMIUM AND IRON FROM CHROME ORE Filed Feb. 1, 1968 I NVE N TOR6 fiyifl'ln- Uko Hnlro M 432211. KAI yalf'a, D. ATTORNEY US. Cl. 23--87 2 Claims ABSTRACT OF THE DISCLOSURE A process for producing chlorides of chromium and iron from chrome ore which comprises the steps of quenching a melt of chromium and iron obtained by fusing and reducing chrome ore together with fluxes and carbon into the form of metal pellets in shot form, packing a reaction column with the pellets, airtightly enclosing the upper portion of the reaction column, flowing hydrochloric acid downward from the top of the column which is kept at an elevated temperature and under pressure with or without simultaneous introduction of hydrogen chloride gas from the top of the column, and collecting the metal pellets in shot form as a mixed solution of chromic chloride and ferrous chloride and, at the same time, exhausting the waste gas from the bottom of the reaction column.

This invention relates to a process for efficiently dissolving and leaching chromium and iron in chrome ore to obtain concentrated aqueous solution of chlorides of such metals and also for producing highly pure metal compounds therefrom. More particularly, the present invention relates to a process for dissolving and leaching chrome ore to produce a concentrated solution of chlorides of chromium and iron by at first dripping molten metal obtained by the smelting of chrome ore into water thereby forming metal pellets in shot form, packing the shot in a long reaction column, supplying hydrochloric acid at an elevated temperature from the top of the column and allowing the acid to flow down therethrough, to collect pure concentrated solution of chromic chloride and ferrous chloride. Very pure crystal of chlorides of chromium and iron may be easily obtained from thus produced solution.

The object of the invention is to provide an improved economic process for producing materials useful for the production of chromium alloys and industrial chemicals.

According to conventional method for extracting chromium in the form of chromium compounds from chrome ores consists of pulverizing chrome ore, heating the pulverized ore together with sodium carbonate or potassium carbonate and lime in a reverberatory furnace, leaching the resulting melt in water thereby to make sodium chromate or potassium chromate, and chromic anhydride or chromic oxide are produced therefrom. The conventional method is relatively suitable for producing chromium salts which may contain either sodium or potassium but is not adapted for producing chromic oxide, and also utilization of iron contents in the starting materials is difficult. In the manufacture of chromium-containing alloys such as stainless steel, it has been in practice to reduce the chrome ore first in an electric furnace together with carbon and fluxes such as limestone and silica thereby to produce an intermediate product called ferrochromium, and then melt the product in an electric furnace together with a given material to obtain a desired chromium-containing alloy such as stainless steel. Acording to such process, chrome United States Patent ice ores must be of high grades having Cr:Fe ratios of at least about 2: 1, but more low grade ores can not be used in this process. A further disadvantage of the prior art is that, because carbon is used in the reduction stage, it has been diflicult to minimize the carbon contents of the product alloys.

The present invention provides a novel process which overcomes the foregoing difiiculties of the conventional methods and which permits not only the production with ease of highly pure chromic chloride and ferrous chloride from any kind of chrome ore, but also complete separation of the chromic chloride and ferrous chloride thus obtained from each other. If necessary, the process of the invention may be combined with any of the known methods so that the hydrochloric gas or hydrochloric acid used may be recovered and reused. The invention will now be described in further details hereunder,

The material to be used in the practice of the invention may be of any grade, high or low. Whatever the grade, the chrome ore is heated and reduced together with carbon and fluxes such as limestone and silica in an elec tric furnace or by other method. All of the magnesium and aluminum contents and most of the silicon content are removed as slags from the ore. Reduced metallic iron and chromium are taken out in the form of molten metal, and the metal is quenched and simultaneously pelletized, as by dripping in water, into the form of shot for use as the starting material. It is preferable that these shot have a size of from 2 to 3 cm. in diameter. This reason is not merely directed to promote the dissolution by increasing the available surface area. Usually carbon and silicon in molten metal tend to form a stable compound with chromium and iron upon slow cooling in an ingot case or the like. Thus resulted metallic mass containing stable carbides and silicides of chromium and iron are extremely insoluble in hydrochloric acid. According to the present invention, formation of any stable carbides and silicides of iron and chromium is prevented by quenching the molten metal such as dripping the molten metal containing carbon and silicon, thus easily soluble materials can be obtained. In the course of the reduction in accordance with the invention, it is not necessary to remove carbon, silicon, phosphorus, sulfur, and the like form the material as in the manufacture of ferrochromium. This is because, even if such impurities are contained in the metal pellets in shot form, carbon and silicon can be completely removed in the subsequent stage of dissolving the metal pellets with hydrochloric acid, and phosphorus and sulfur, if any in the solution, can be simply removed afterwards. This will be further described in Example 1. Acordingly, the cost required for the reduction of chrome ore can be relatively low.

Now, the metal pellet formed from the reduction of chrome ore is dissolved in hydrochloric acid while generating hydrogen. However this operation would prove most ineflicient when carried out in batch system. Even with the material in shot form, the batch operation would be practically of no industrial significance.

With this in view, the present inventor made diversified studies in search of a method which would permit rapid dissolution of metal pellets of chromium and iron in hydrochloric acid and also increases in the concentrations of chromic chloride and ferrous chloride in the solution. The results obtained have led to the present invention, which will now be described in further detail referring to the figure in the accompanying drawing.

The drawing is a diagrammatic general view of a form of apparatus for use in the invention which is adapted for dissolving and leaching a metal in shot form which contains chromium and the like with hydrochloric acid thereby obtaining the chromium and the like in the form of chlorides thereof.

An acid-proof reaction column 7 having a perforated plate 9 and a reacted solution reservoir 11 in the lower part thereof is packed with metal pellets in shot form 8 which are supplied through an airtightly scalable opening provided for that purpose on top of the column. From an inlet 6 provided also on top of the column, hydrochloric acid is introduced and allowed to flow down. A tank 1 for hydrochloric acid connected to the inlet 6 is equipped with a safety valve 2 which is in direct communication with the reaction column 7 for the regulation of the pressure therein. It is now assumed that steam is supplied to the column via a duct 3 to heat the interior of the column to a temperature above 70 C., preferably between 80 and 90 C., and hydrochloric acid is allowed to flow down into the column. A reaction will then proceed between the hydrochloric acid and metal pellets in shot form. A reacted solution will be collected in the reservoir 11 and separated through an outlet 12. Waste gas is discharged through an exhaust port 10, drain reservoir 13, and exhaust duct 14.

In the practice of the invention, an increased elficiency can be attained by supplying hydrogen chloride gas from the top of the column as indicated at 4 simultaneously with the flowing down of hydrochloric acid from the top of the column. With such arrangement the metal shot would be thoroughly washed on the surface and the surface area to contact with the acid or hydrogen chloride which flows down would be increased, thereby high concentrated solution of chromic chloride and ferrous chloride would be obtained.

Particularly important considerations in the dissolution of metal pellets in shot form with hydrochloric acid in the reaction column may be boiled down to the following two. First, the reaction in the reaction column should be carried out with the application of heat. While the suitable temperature range is from 70 to 150 C., a temperature between about 80 to about 90 C. is preferred. At a temperature below 70 C. the reaction would not proceed smoothly. Above 150 C. other troubles would take place. Various heating means may be adopted including electrical heaters. For the heating purpose, steaming is convenient, particularly when the steam is supplied from the top of the reaction column. Second, the gases in the reaction column should be urged downward. To attain this end, the upper portion of the reaction column must be airtightly enclosed and an exhaust port for the gas must be provided in the lower portion of the column. Accordingly, when hydrochloric acid is to be flown down from the top of the reaction column, hydrogen chloride gas should also be blown in from the top of the column. The same is true of blowing of steam into the vessel.

If any of the above requirements is not met, the reaction would not take place smoothly. For example, if hydrogen chloride gas and steam are blown upward from the bottom of the column, though hydrochloric acid is blown down as above, the acid would be prevented from flowing down and retained in the column by the pressure of the gas or steam which comes upward when the metal pellets in shot form have dissolved to a granular state. This would eventually make it impossible to flow down the acid to the bottom of the column and to supply the steam to the upper portion of the column, thus to cool the column to a too low temperature for the reaction. In the present invention, therefore, the column is hermetically enclosed on the upper portion and the pressure produced by hydrogen chloride gas and steam blown in from the top of the column is utilized to smoothen the downward flow of the acid, whereby a high concentrated solution of chromic chloride and ferrous chloride can be obtained efficiently.

The present invention provides a novel process for isolating both chromic chloride and ferrous chloride in crystal form from the solution obtained above which contain the chlorides of chromium and iron. The reacted solution taken out of the reaction column is a mixed solution of FeCl and CrCl Into this solution is blown an oxidant, e.g., air or C1 gas, to convert FeCl into FeCl and CrCl into CrCl Next, hydrogen chloride gas is blown in, thus concentration of the hydrochloric acid is increased until CrCl is crystallized. The product is filtered and CrCl is separated. FeCl in the filtrate is reduced to FeCl with iron scrap or other suitable reducing agent. As hydrogen chloride gas is blown in, the concentration of hydrochloric acid is increased and FeCl is deposited in crystal form. After the separation of the crystals the filtrate is returned to the reaction column and is again flown down from the top of the column for reuse in the dissolution of metal pellets in shot form.

EXAMPLE 1 Nineteen kilograms of chrome ore (48.5% Cr O 24% Fe O 18% SiO 6% C1 0 and 3% MgO) was reduced with about 4.5 kg. of coke in the presence of about 3 kg. of limestone, and about 1 kg. of silica, in an electric furnace at about 1600 C. All of the aluminum and magnesium contents and most of the silicon content were removed as slags. The molten metal was quenched by dripping into water, when 10 kg. of metal pellets in shot form of the following composition was obtained:

Percent Cr 58.6 Si 5.1 C 7.3 Fe 28.8

tion was obtained. The datas were as follows:

Material consumption (g./hr.) Amount of eflluent (l./hr.) 1.3 Cone. of effluent (g./l.):

Cr 60.5 Fe 29.5 0.3

Steam supply (l./hr.)

By this way, 1.5 to 2 tons of shot could be extracted in one day, whereas with conventional process it needs about 5 days.

The mixed solution obtained in this way may be di rectly used as a starting material for processes which themselves are known, for example for the manufacture of chromium-containing alloys or metal salts of chromium and iron.

Taking the manufacture of 18-chrome alloy as an example, a chloride solution prepared by the above procedure (contg. 60.5 g./l. Cr and 29.5 g./l. Fe) is filtered to remove Si, C and other insolubles. To the filtrate, a separately prepared chloride of Fe is added up to a CrzFe ratio of 18:82. With thorough stirring, the mixture is roasted by a spray roaster to form a solid solution of mixed oxides of Fe and Cr. This solid solution upon reduction with a suitable reducing agent such as hydrogen will yield 18-chrome alloy powder, permitting at the same time the recovery of the hydrogen chloride gas used, in the manner as is well known to the art. In such case, lowgrade chrome ores usually deemed worthless may be used. Also, carbonless 18-chrome alloys can be produced with the use of hydrogen as the reducing agent.

In the case when phosphorus or sulfur is present in the chloride solution to be used as the starting material, it is necessary to remove sulfur beforehand by converting it into CaSO whereas no pretreatment is needed for removal of phosphorus because it will escape from the material on roasting and will not find its way into the product alloy.

It is already known that, in the manufacture of metal salts, a suitable organic solvent such as ether may be added to a chloride solution prepared as above, thereby was diluted with water and the concentration of hydrochloric acid was kept at about in order to facilitate the reduction with iron dust. Then, again hydrogen chlo ride gas was introduced and the solution was saturated with the gas. The datas were as follows:

{Time (min) to dissolve the iron content into the ether for subsequent isolatoin of ferrous chloride and chromic chloride. The concentration of hydrochloric acid in such case is approximately 6 N. The ether which contains ferrous chloride is recovered by distillation, and from the chromic chloride and ferrous chloride obtained as the distillation residue, one can obtain chromic oxide, ferrous oxide, and hydrogen chloride gas, as above described.

EXAMPLE 2 About 7 kg. of metal pellets in shot form produced in the same manner as described in Example 1 was packed in a reaction column which was exactly same as that used in Example 1. Steam was blown in from the top of the column to heat the charge in the column to a temperature ranging from 80 to 90 C. Also from the top of the column an aqueous solution of hydrochloric acid (1:1) was flown down at a rate of one liter per hour. At the same time, hydrogen chloride gas was blown in from the top of the column at a rate of 0.3 liter per minute. A clear chromium-containing chloride solution was obtained from the bottom of the column. The datas were as follows:

Material consumption (g./hr.) 161 Amount of effluent (l./hr.) 1.3 Cone. of efiluent (g./l.):

Cr 94 Fe 46 Steam supply (l./hr.) 0.3

By filtering the chloride solution obtained by the above procedure, C and Si were removed together with other insoluble matters. Into the filtrate C1 gas was blown in thereby to oxidize the FeCl in the solution into FeCl At this time, when the chromic chloride was left in the form of CrCl the rate of crystallization of chromium was increased upon the subsequent introduction of hydrorgen chloride gas but CrCl was readily oxidized into CrCl The solution was saturated with HCl gas and thus CrCl was deposited in crystal form. The datas were as follows:

The crystals of FeCl was centrifuged and washed with cc. of concentrated hydrochloric acid. 350 cc. of the reacted solution included 40 cc. of the concentrated hydrochloric acid used for the washing purpose. The FeCl crystals was white and elemental analysis showed that it consisted of 99.6% Fe and 0.4% Cr. The 0.4% Cr was presumably attributed to the deposition of the solution of CrCl The crystals of CrCl and FeCl thus obtained was again thoroughly washed with hydrochloric acid, thus the Fe content of Cr and the Cr content of Fe could be reduced to the degree ef 0.0%. From these CrCl and FCl2, oxides could be formed as already described.

Now that the present invention has been described in detail hereabove, the effects of this invention which can be thereby achieved will be summarized as hereunder.

(1) Since the material ore is reduc d with heat, together with fluxes such as limestone and silica, in an electric furnace or by other means, all of the magnesium. and aluminum contents and most of the silicon content of the ore can be removed as slags. Other impurities can also be removed in simple manner in subsequent stages. Accordingly, high pure chromic chloride and ferrous chloride can be produced with ease.

(2) It is not necessary to pulverize the material ore because the ore is reduced together with fluxes such as limestone and silica, in an electric furnace or by other means, and the molten metal thus obtained is quenched as by dipping into water to a shot form and the resultant in the form of a metal shot readily soluble in hydrochloric acid is packed in a reaction column and dissolved as chromic chloride and ferrous chloride. Moreover, the solution can be prepared with a high efficiency to high concentrations of the contents with an economical advantage.

(3) Even though the metal pellets in shot form packed in the reaction column is dissolved into granular form, the pressure of steam or hydrogen chloride gas which is blown in from the top of the column, which is required only to be a slight pressure, will smoothen the fiow of the effluent and promote the reaction.

The crystals of CrCl was centrifuged and washed with 40 cc. of concentrated hydrochloric acid. 350 cc. of the reacted solution included 40 cc. of concentrated hydrochloric acid used for the washing purpose. The crystals were light purple in tint, and elementary analysis showed that it consisted of 99.9% Cr and about 0.1% Fe which was presumably attributable to the deposition of the FeCl solution. The rate of crystallization of CrCl was about 57.7% of the total Cr content of the solution before and after the reaction.

After the removal of CrCl crystals by filtration, iron dust was added to the filtrate thereby to reduce FeCl to (4) When the solution of chromic chloride and ferrous chloride is roasted in a spray roaster to a mixed oxide of Fe and Cr, hydrochloric acid can be recovered. It therefore is possible to recover and reuse almost all of the acid which is used in the practice of the invention, thus realizing material economy.

. (5) Since the salt solution used in the invention is a chloride solution, more economical advantages are attained in respect of equipment, calorific amount, etc. for the recovery and reuse of the acid than those derivable from the dissolution of sulfuric acid or nitric acid.

(6) For the production of chromium alloys, e.g., 18-

FeCI At this time, the filtrate with a high acid value chrome and 13-chrome alloys, chrome ores of low grades,

for example, with less than about 30% Cr O which have heretofore been left abandoned as worthless, can be utilized as useful material without any hindrance and with a corresponding saving in cost.

We claim:

1. A process for producing chlorides of chromium and iron from chrome ore, which comprises the steps of quenching a melt of chromium and iron obtained by fusing and reducing chrome ore together with fluxes and carbon into the form of metal pellets in shot form, packing a reaction column with the pellets, airtightly enclosing the upper portion of the reaction column, flowing hydrochloric acid downward from the top of the column which is kept at an elevated temperature and under pressure to obtain a mixed solution of FeCl and CrCl oxidizing this mixed solution with an oxidant by blowing the oxidant into the mixed solution to convert the FeCl into FeCl and the CrCl into CrCl introducing hydrogen chloride gas into the solution until CrC1 is crystallized out, filtering the mixture of said solution and crystallized CrCl to separate the CrCl and to obtain a filtrate, reducing the FeCl in the filtrate with a reducing agent to FeC1 and thereafter introducing hydrogen chloride gas into the filtrate until the FeCl is deposited in crystal form.

2. A process for producing chlorides of chromium and iron from chrome ore, which comprises the steps of quenching a melt of chromium and iron obtained by fusing and reducing chrome ore together with fluxes and carbon into the form of metal pellets in shot form, packing a reaction column with the pellets, airtightly enclosing the upper portion of the reaction column, flowing hydrochloric acid downward from the top of the column which 8 is kept at an elevated temperature and under pressure with simultaneous introduction of hydrogen chloride gas from the top of the column to obtain a mixed solution of FeCl; and CrC1 oxidizing this mixed solution with an oxidant by blowing the oxidant into the mixed solution to convert the FeCl into FeCl and the CrCl into CrCl introducing hydrogen chloride gas into the solution until CrCl is crystallized out, filtering the mixture of said solution and crystallized CrC1 to separate the CrC1 reducing the FeCl in the filtrate with a reducing agent to FeCl and thereafter introducing hydrogen chloride gas into the filtrate until the FeCl is deposited in crystal form.

References Cited UNITED STATES PATENTS 1,054,400 2/1913 Dow et a1. 23--87 1,814,360 7/1931 Berresford 23-87 1,814,392 7/1931 LOW et a1. 2387 1,938,461 12/1933 Prutton 23-87 2,573,935 11/1951 Stutzman 26413 2,677,598 5/ 1954 Crummett et a1 2387 2,752,301 6/1956 Cooper 23-87 XR 2,762,700 9/1956 Brooks -.5 3,244,512 4/1966 Gravenor 2387 XR FOREIGN PATENTS 269,028 4/ 1927 Great Britain.

EDWARD STERN, Primary Examiner US. Cl. X.R. 

